Chrome ore treating process



United States Patent 3,144,322 CHROME ORE TREATING PROCESS Frederick E. Bacon and Howard M. Dess, Niagara Falls,

N.Y., assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed Nov. 7, 1961, Ser. No. 150,627 6 Claims. (Cl. 75-1) The present invention relates to process for the removal of iron from chrome ore. More particularly, the present invention relates to the treatment of high-iron content chrome ore whereby the ore is rendered suitable for use in the manufacture of refractory bricks.

Chrome ore is widely utilized in combination with magnesia as a constituent material in the manufacture of various types of refractory bricks which are used in the construction of open hearth steel-making furnaces. The proportion of magnesia combined with the chrome ore in these bricks often ranges between 30 and 70 percent depending on the particular characteristics desired in the bricks which may be manufactured by any of several known techniques, e.g., by casting a molten mixture of ore and magnesia, or by bonding or sintering fused grains of chrome ore and magnesia.

However, in view of the fact that many readily available and relatively inexpensive chrome ores contain substantial amounts of iron as oxide, e.g., up to 26 percent (expressed as FeO), and in view of the fact that the corrosion-resistant properties of chrome ore-magnesia refrac tory bricks in open hearth furnace operations are adversely affected in proportion to the amount of the contained oxidic iron material, it has been a continuing problem to provide economical and convenient methods for reducing the iron content of chrome ores.

Moreover, since it is often highly important in the production of refractory bricks from chrome ore and magnesia to both reduce the iron content of the chrome ore and enrich the ore with magnesia, it is clear that it would be a substantial benefit if both of these requirements could be accomplished in a single operation.

It is therefore an object of the present invention to provide a process for reducing the iron content of chrome ore.

It is another object of the present invention to provide a process for reducing the iron content of chrome ore while, in the same operation, enriching the ore with magnesia.

Other objects will be apparent from the following description and claims.

A particular embodiment of a process in accordance with the present invention comprises mixing chrome ore with hydrated magnesium chloride; heating the mixture in a temperature range between about 800 C. and 1400 C. to thereby decompose the hydrated magnesium chloride and chlorinate at least a portion of the iron contained in the ore; and continuing the heating of the mixture in the temperature range of 800 C. to 1400 C. until the chlorides resulting from the chlorination of iron in the ore are volatilized from the mixture and until the magnesium in the mixture is converted to magnesia.

In the practice of the present invention, a mixture of chrome ore with hydrated magnesium chloride is prepared in finely divided form or as pellets. The amount of hydrated MgCl in the mixture is not critical although increasing amounts of hydrated MgCl admixed with 3,144,322 Patented Aug. 11, 1964 chrome ore, up to about a 1:1 ratio by weight, provide increased iron removal. The preferred amount of hydrated MgCl is that which, upon conversion to MgO, is suflicient to enrich the magnesia content of the ore by a predetermined amount as required in the subsequent manufacture of refractory bricks.

That is to say, in the preferred form of the present invention, up to the total amount of magnesia (MgO) required to be combined with the chrome ore is provided through the addition of hydrated MgCl After being mixed, the chrome ore and hydrated MgCl are heated in a suitable furnace, preferably in a deep bed, at a temperature in the range of about 800 C. to about 1400 C. During the heating, the hydrated MgCl decomposes and the HCl which is thereby liberated selectively reacts with the oxidic iron contained in the ore. The resulting iron chlorides are volatilized and removed from the mixture with a consequent lowering of the iron content of the ore. The remaining constitutents of the ore are substantially unaffected by the liberated HCl. The heat treatment of the reaction mixture is continued until substantially all of the magnesium chloride in the mixture has been converted to MgO. This condition is generally achieved by the time that evolution of iron chloride vapors from the mixture can no longer be visually detected.

The preferred temperature for the heat treatment of the chrome ore-magnesium chloride mixture is about 1300" C. since at this temperature the formation of HCl and the residence time thereof in the mixture provides a high level of iron removal together with magnesia formation.

After the iron content of the ore has been reduced by volatilization of the chlorides, the resulting magnesiaenriched chrome ore is suitable for use in accordance with known techniques in the manufacture of refractory bricks. For example, the magnesia enriched chrome ore can be subjected to additional heating at an increased temperature to provide a fused refractory material. Alternatively, the iron-depleted and magnesia-enriched ore can be heated to the molten state and cast into fused refractory bricks.

The following examples are provided to illustrate the present invention:

Example I Hydrated magnesium chloride, MgCl-6H O, and chrome ore were mixed in a 1:1 ratio by weight and formed into pellets inch in diameter and A to /2 inch long.

The chromium to iron ratio in the pelletized mixture was 1.56.

The composition of the chrome ore was as follows:

Percent CI'203 .9 FeO 25.9 SiO 1.13 A1 0 16.78 M g0 9.93

A magnesia crucible was heated in air up to a temperature of about 900 C. and the pellets were dropped into the hot crucible. There was no visible evidence of chlorination although heating was continued for 14 minutes.

The material in the crucible was withdrawn and analyzed. The results of the analysis are as follows:

Cr O percent 36.4 FeO do- 19.6

CrzFe 1.50 MgO "percent" 22.6

The results of Example I show that very little iron re-- moval was achieved at the operating temperature em-- ployed.

Example II The same materials, equipment and procedure wereused as in Example I except that the heating temperature was 1100 C.

Under these conditions fuming was observed in the crucible and heating was continued until the fuming stopped. The material in the crucible was withdrawn and analyzed. The results of the analysis are as follows:

Cr O percent 36.4 FeO do 17.01 Cr:Fe 1.88 MgO percent 25.7

Example III The same materials, equipment and procedure were used as in Example I except that the heating temperature was 1300 C.

Under these conditions fuming was observed in the crucible and heating was continued until the fuming stopped. The material in the crucible was Withdrawn and analyzed. The results of the analysis are as follows:

Cr O percent 38.2

FeO do 14.35

CrzFe 2.34

MgO percent 28.2 Example IV The same materials, equipment and procedure were lows:

Cr O percent 33 .1 FeO do 12.76 CrtFe 2.27 MgO percent 37.4

The results of Example IV show that increasing the magnesium chloride-chrome ore mixture above a 1:1 ratio does not provide increased iron removal.

In a further embodiment of the present invention, the iron content of chrome ore is very substantially reduced by the use of anhydrous HCl, although in this case magnesia-enrichment is not obtained.

In this embodiment, a bed of particulated chrome ore is treated with anhydrous HCl at temperatures in the range of about 500 C. to about 1400 C., under which circumstances a substantial amount of the contained iron is chlorinated and converted to chloride and evolved from the bed with consequent lowering of the iron content of the ore. The preferred operating temperature to provide optimum iron removal is about The following example will illustrate the above-described process.

Example V Anhydrous l-ICl gas was passed through a bed of particulated chrome ore which was located in a magnesia crucible inductively heated in air to a temperature of about 500 C. The composition of the ore was as in Example 1.

Yellow fumes were observed evolving from the orebed while the temperature was at about 500 C. The temperature was increased to between 1130 C. and

4 1170 C. and maintained at this value for 2 hours and 10 minutes. At this time yellow fumes were still evolving from the ore-bed. However, the process was interrupted temporarily and a sample of the ore was analyzed. The analysis showed the following results:

Cr O percent 46.5 FeO d0 11.70 CrzFe 3.5

After analysis the above treatment was continued for an additional two hours. Further analysis at this time showed the following results:

'Cr O percent 41.2 FeO do 4.59 CrzFe 7.9

It can be seen from the foregoing disclosure that novel and beneficial process is provided by the present invention for the up-grading of chrome ore whereby the utility of the ore in the manufacture of refractory bricks is materially enhanced.

What is claimed is:

1. A process for reducing the iron content of chrome ore and for enriching the magnesia content of the ore which comprises heating a mixture of chrome ore and hydrated MgCl at a temperature in the range between about 800 C. and 1400 C. to thereby decompose the hydrated MgCl and chlorinate at least a portion of the iron contained in the ore; and continuing the heating of the mixture in the temperature range of about 800 C. to about 1400 C. until iron chlorides resulting from the chlorination of the ore are volatilized from the mixture and until the magnesium in the mixture is converted to magnesia.

2. A process in accordance with claim 1 wherein the heating is conducted at a temperature of about 1300 C.

3. A process for reducing the iron content of chrome ore and for enriching the magnesia content of the ore which comprises mixing chrome ore with hydrated mag nesium chloride, the hydrated magnesium chloride being in an amount sufiicient to provide, upon the thermal decomposition thereof, a predetermined amount of MgO for enriching the ore; heating the mixture in a temperature range between about 800 C. and about 1400 C. to thereby decompose the hydrated magnesium chloride and chlorinate at least a portion of the iron contained in the ore; and containing the heating of the mixture in the temperature range of 800 C. to 1400 C. until iron chlorides resulting rom the chlorination of iron in the ore are volatilized from the mixture and until the magnesium in the mixture is converted to magnesia.

4. A process for reducing the iron content of chrome ore and for enriching the magnesia content of the ore which comprises heating, in air, a mixture of chrome ore and hydrated MgC1 at a temperature in the range between about 800 C. and 1400 C. to thereby decompose the hydrated MgCl and chlorinate at least a portion of the iron contained in the ore; and continuing the heating of the mixture in the temperature range of about 800 C. to about 1400 C. until iron chlorides resulting from the chlorination of the ore are volatilized from the mixture and until the magnesium in the mixture is converted to magnesia.

5. A process in accordance with claim 4 wherein the heating is conducted at a temperature of about 1300" C.

6. A process for reducing the iron content of chrome ore and for enriching the magnesia content of the ore which comprises mixing chrome ore with hydrated magnesium chloride, the hydrated magnesium chloride being in an amount sufiicient to provide, upon the thermal decomposition thereof, a predetermined amount of MgO for enriching the ore; heating the mixture, in air, in a temperature range between about 800 C. and about ALL 1400 C. to thereby decompose the hydrated magnesium chloride and chlorinate at least a portion of the iron contained in the ore; and continuing the heating of the mixture in the temperature range of 800 C. to 1400 C. until iron chlorides resulting from the chlorination of iron in the ore are volatilized from the mixture and until the magnesium in the mixture is converted to magnesla.

References Cited in the file of this patent UNITED STATES PATENTS Queneau Apr. 30,

Erasamus Aug. 30,

Copper June 26,

FOREIGN PATENTS Canada Nov. 23,

Canada Dec. 29, 

1. A PROCESS FOR REDUCING THE IRON CONTENT OF CHROME ORE AND FOR ENRICHING THE MAGNESIA CONTENT OF THE OIRE WHICH COMPRISES HEATING A MIXTURE OF CHROME ORE AND HYDRATED MGCL2 AT A TEMPERATURE IN THE RANGE BETWEEN ABOUT 800*C. AND 1400*C. TO THEREBY DECOMPOSE THE HYDRATED MGCL2 AND CHLORIMATGE AT LEAST A PORTION OF THE IRON CONTAINED IN THE ORE; AND CONTINUING THE HEATING OF THE MIXTURE IN THE TEMPERATURE RANGE OF ABOUT 800*C. TO ABOUT 1400*C. UNTIL IRON CHLORIDES RESULTING FROM THE CHLORINATION OF THE ORE ARE VOLATILIZED FROM THE MIXTURE AND UNTIL THE MAGNESIUM IN THE MIXTURE IS CONVERTED TO MAGNESIA. 